The present invention relates to a method of prevention or treatment of restenosis by irradiation and, more particularly, to a method of treatment of restenosis by external stereotactic irradiation.
The most common therapy for ischemic heart disease is percutaneous transluminal coronary angioplasty, or "balloon" angioplasty, in which a constricted coronary artery is dilated by the insertion of a balloon. One complication of this therapy is that restenosis, or recurrent narrowing, occurs in 30%-40% of dilated arteries. To prevent this, a stent often is implanted in the dilated segment. As a foreign material, the stent induces the proliferation of smooth muscle cells in the vessel walls, so that the restenosis is not eliminated, but is only reduced to about 20%. Therefore, the implantation of the stent may be supplemented with radiotherapy, in which a radioisotope is inserted into the dilated segment or into the implanted stent in order to prevent the proliferation of the smooth muscle cells. This is time consuming, requires costly safety arrangements in the catheterization laboratory, should be performed during invasive catheterization, presents a problem of non-homogeneous irradiation of the dilated segment and adjacent segments (depending on centralization of the radioisotope) as well as different vessel wall layers, and has logistical problems because of the short half life (order of days to months), and consequent short shelf life, of the radioisotopes.
Stereotactic radiotreatment is a recognized therapy for deep seated brain tumors. See, for example, Wendell Lutz, Ken R. Winston and Nasser Maleki. "A system for stereotactic radiosurgery with a linear accelerator", Int. J Radiation Oncology Biol. Phys. Vol. 14 pp. 373-381 (1988). In this mode of therapy, beams of ionizing radiation, typically gamma radiation from a radioisotope such as .sup.60 Co or from a linear accelerator, are directed at the tumor from several angles. All the beams pass through the tumor, but each beam passes through a different portion of the tissue outside the tumor. In this way, a therapeutic dose of radiation is delivered to the tumor without damage to the surrounding tissue.
In order for stereotactic radiotreatment to succeed, the location of the target of the treatment must be known precisely, and the radiation source must be aimed precisely at the target. This is possible in the case of brain tumors, which are fixed in position relative to the patient's head, and whose location can be determined by non-invasive means, but not in the case of moving targets such as coronary arteries. Therefore, it has not been possible heretofore to treat restenosis with stereotactic radiotreatment, despite the advantages that such treatment would have over the present method of radioisotope insertion or implantation.
There is thus a widely recognized need for, and it would be highly advantageous to have, a method of stereotactic radiotreatment or prevention of restenosis.